My GF had a lot of trouble with telus on her 3GS, as far as losing signals outside on the streets (Rene-Lvesque, sainte-Catherine, st-Denis) and telus sed to tell her that it was because of the buildings that were making interference....

That said about a month ago she updated to the 4s and has yet to experience any problem (the 3GS had problem daily not to say every hour or so)